Process of making safety paper



Patented July 3, 1934 PROCESS OF MAKING SAFETY PAPER Frank S. Wood, Quincy, Mass.

No Drawing. Application July 22, 1931, Serial No. 552,550

1 Claim.

By bi-functional step is meant of or belonging to two proper omces or works of an agent which, in the manufacture of paper, has heretofore had but one ofiice. For example, the onice of a sizetub is to size the paper. By adding to it the oflice of chemically treating the paper with the same operation as the sizing, the liquid mixture is given two functions; my invention gives it a double action of an entirely different nature which is therefore a bi-functional step in the paper making process.

This invention relates to so called safety papers and to the processes of making such papers so that when written on with ink, the writing cannot be removed, altered or replaced without setting the ink in such writing or leaving telltale stains, discolorations or alterations visible on the surfaces of such paper, or both.

Its salient purpose is to provide an alternative step or improvement in a process of making safety paper by one continuous operation over that for which my application for a patent was filed November 8, 1930, Serial Number 494,443. Its other purpose is for an improved bi-func- -tional step in other processes of making safety papers that are not one continuous operation.

The novelty consists in the simultaneous application to a web of paper of a chemical inkset composition made up of ferrocyanide of potassium and carbonate of potassium dissolved in water so as to give a moderate alkalinity to a normally acid paper and varying in porportions with different grades and colors of paper but having a delicate balance which not only im- Ipregnates the paper with inksetting power but also sizes the paper to the degree required for a good writing surface. For further details, see my specification for a safety paper filed Apr. 22, 1931, Ser. No. 532,115. When, however, this suriface is written upon with ink and a prolonged application of chlorine has been made for the purpose of bleaching the ink, then the delicate balance is evidenced by the fact that the chlorine dissolves or breaks down the sizing and the paper is ruined for writing purposes for the reasons that it not only spoils the surface of the paper and makes the ink feather but it also changes the color of the same re-written ink, thus furnishing obvious and various means of detecting that the writting has been tampered with. In combination with another liquid tub sizing application necessary or desirable in the fabrication of paper, in the surface coloring of paper, either or both. Tub-size is made of starch, glue and wax, at present; other materials may here- (Cl. ill-457.95)

produces a better inkset than has heretofore been obtained by other methods including expensive machines for chemically treating the paper.

It is well known that the sizing of paper produces a sort of delicate layer of varnish upon its surface that results in the desired writing finish.

I have discovered that by using a given proportion of my inkset liquid in place of that same proportion of water in the sizing, the sizing solution is not injured. Therefore, by mixing my inkset liquid which is a chemical composition with the sizing, in the application of this mixture, the paper absorbs both the sizing and the inksetting liquid at one and the same operation.

I have also discovered that by using a given proportion of my inkset liquid in place of the same amount of water in the mixing of dyes or so called fugitive ink, the dyes are not injured. Therefore, by mixing my inkset liquid with the dye which is to be applied to white paper for the purpose of coloring its surfaces, the paper is also impregnated with my inkset composition at one and the same operation.

Both discoveries constitute a bi-functional step in the process of manufacturing either a white safety paper as it is being run through a papermaking machine, or a colored safety paper of the La Monte or Hammermill type at the same time that the tint and design is being applied to the surfaces of the latter. This obviates the necessity of installing a separate machine for applying the inkset treatment to the web of paper either as a continuous or a rehandling operation.

I will first describe the application of my invention to the making of safety paper by one continuous operation. The paper as it is being made on the Fourdrinier machine is dried out and, while hot, is taken down into a tub under a roll immersed in a liquid mixture composed of sizing and inkset solution kept at a desired constant temperature; the hot, porous paper absorbs enough of the sizing to supply the proper writing surface and at the same time absorbs enough of the inkset solution mixed with the sizing to give the paper the power of setting ink written on its surface when ink eradicator is applied for Such the purpose of removing the writing. Then the paper goes to other drying rolls, thence to the calender where it is finished and thence to the reel where it is wound up as safety paper, at one continuous operation.

In the application of my invention to the other type of safety paper process, when the web of paper is run through a suitable container filled to its desired level with colored water mixed with a predetermined amount of my inkset solution, the paper absorbs the moisture of the liquid mixture, colors both surfaces of the web of paper and passes on between rolls that utilize the tint to impress some form of design upon the surfaces of the paper; while this is taking place, the paper is also absorbing inkset solution. Then, the paper is dried by whatever method is in use at that particular plant and is ready to be rewound into reels or to proceed to the cutting machines, according to the system prevailing.

For the purpose of my present invention it is not believed to be necessary to set forth either the many formulas for giving the inkset feature to innumerable grades and makes of paper that vary accordingly as well as with different colors and makes of dyes. It is obvious that these are almost infinite for the reason that the same grade of paper made at a different mill requires a different formula, and each different grade as well. Again a 10% inkset solution of a given strength in 90% of sizing or colored water may be made equal to another 20% solution by using double the quantity of chemicals for the same volume of inkset solution. I have taken this up in specific instances in other preceding pending patents. A proper balance of the mixture may be had either by keeping the sizing constant in strength and varying the proportions of the chemical inkset solution until the desired attributes are obtained in a given make or grade of paper, or by increasing or decreasing the strength of the chemical solutions without changing their proportions. Again, the strength of the sizing may be increased or decreased as well as the variation in proportions; and it may be found desirable, in certain kinds of paper, to do both.

One of the formulas which I have used with good results calls for a unit volume of mixture composed of sizing and 20% chemical solu tions. I have had an equally good result by using 50% colored water and 50% chemical solutions. Various proportions of inkset solutions must necessarily be employed, for dyes vary in strength both as to color and make; and, regardless of color, the same grade of white paper made by different manufacturers, requires different formulas. Therefore, it is clear that the variations in papers themselves, in their sizing and in their dyes, demand various proportions in the amount and strength of inkset or chemical solutions without departing from the spirit of my invention.

What I therefore claim and desire to secure by Letters Patent is:

In a process for making safety paper by one continuous operation, a bi-functional step comprising ink set solutions and sizing in such proportions that the ink setting chemioals do not interfere with the proper sizing of the paper, and the sizing does not interfere with the transmuting of ordinary paper into safety paper when both sizing and ink setting solutions are mixed together and applied to a web of hot, dry paper in the same bi-functional step, and without changing the normal color of the paper.

FRANK S. WOOD. 

